1. Field of the Invention
The invention relates to automatic transmission torque converter reactors having integral, segmented thrust washers on the reactor hub and a method for concurrently shaping, surface finishing, and surface hardening the thrust washers for improved wear resistance and hydrodynamic lift.
2. Description of Related Art
Certain automatic transmission torque converter reactors are fabricated by injection molding phenolic resin to a desired complex reactor configuration having a reactor hub with an integrated segmented thrust washer. The raised thrust washer segments are trapezoidal in shape and are arranged circumferentially on an axial end face of the reactor hub as shown in FIG. 1. The thrust washer segments include axial end surfaces that collectively define a reactor thrust bearing that cooperates with a counterface, typically a low carbon powder metallurgy steel turbine hub of the torque converter assembly. The axial end surfaces of the washer segments are provided with a curvilinear profile to provide hydrodynamic lift relative to the turbine hub.
In attempts to increase the performance envelope of certain automatic transmissions and reduce cost, die cast aluminum-alloy torque converters have been evaluated to replace molded phenolic resin torque converters used heretofore in automatic transmissions. However, die cast aluminum alloy torque converter reactors with integrated thrust washer segments exhibit increased segment surface roughness and have less desirable segment surface profiles when compared to molded phenolic counterparts. Moreover, the segments exhibit variable shapes due to inadequate metal casting precision. Applicants have discovered through dynamometer test evaluations of such die cast aluminum torque converter reactors operated with a steel turbine hub that die cast aluminum reactors suffered excessive wear on the thrust surfaces, evidenced by loss of the as-fabricated profile and excessive grooving of the thrust surfaces of the reactor thrust washer segments and a reduction in height of the segments to less than 20% of their initial design height. Such excessive wear and deterioration was attributed to metal-to-metal contact between the aluminum thrust washer segments and the turbine hub. This problem of wear and deterioration effectively rendered the die cast aluminum alloy torque converter reactors unacceptable for use. In one solution to the problem, needle bearing assemblies have been positioned between the reactor thrust face and the turbine hub in certain automatic transmissions to reduce the severity of contact.
Thus, there is a need for a surface treatment for a cast metallic torque converter reactor in a manner to impart improved wear resistance and hydrodynamic lift to the reactor thrust washer segments and permit use of the cast metallic torque converter reactor without the need for costly needle bearings.